Plasma reactor for processing a workpiece with an array of plasma point sources

ABSTRACT

A plasma source consisting of an array of plasma point sources that controls generation of charged particles and radicals spatially and temporally over a user defined region.

BACKGROUND

Technical Field

The disclosure concerns plasma processing of a workpiece such as asemiconductor wafer, and reduction in process non-uniformities.

Background Discussion

In conventional plasma processing, the processed wafers may suffer fromlocal non uniformities—due non-uniform stress, non-uniform filmcomposition (for a deposition process), non-uniform CD's (criticaldimensions of features) due to different etch environments. This couldbe due to differences among incoming wafers or differences in thecharacteristic of the processing chamber (e.g., in a carousel styleprocessing chamber where the rotating wafer sees a leading edge and atrailing edge radical dwell time difference or different localtemperature).

SUMMARY

A plasma reactor comprises: a processing chamber and a workpiece supportin the processing chamber, the chamber comprising a lower ceiling facingthe workpiece support; an upper ceiling overlying and facing the lowerceiling and a gas distributor overlying the upper ceiling; plural cavitywalls defining plural cavities between the upper and lower ceilings, thegas distributor comprising plural gas flow paths to respective ones ofthe plural cavities; plural outlet holes in the lower ceiling alignedwith respective ones of the plural cavities; and respective powerapplicators adjacent respective ones of the plural cavities, a powersource, plural power conductors coupled to respective ones of the powerapplicators, and a power distributor coupled between the power sourceand the plural power conductors.

In one embodiment, the plural cavity walls comprise dielectric cavitywalls.

In a further embodiment, the power source comprises an RF powergenerator and wherein each one of the respective power applicators isseparated from an interior of a corresponding one of the plural cavitiesby the corresponding one of the plural cavity walls.

In one embodiment, the power applicator comprises an electrode forcapacitively coupling RF power into the corresponding one of the pluralcavities. In this embodiment, each electrode may surround a section ofthe corresponding one of the plural cavities.

In another embodiment, the power applicator comprises a coil antenna forinductively coupling RF power into the corresponding one of the pluralcavities. In this embodiment, the coil antenna may comprise a conductorcoiled around a section of the corresponding one of the plural cavities.

In a yet further embodiment, the power source is a D.C. power generator,each one of the power applicators comprises an electrode for D.C.discharge, and wherein each one of the dielectric cavity walls isconfigured to expose the corresponding electrode to the interior of thecorresponding one of the plural cavities.

In one embodiment, the power distributor comprises plural switchescoupled between an output of the power generator and respective ones ofthe power conductors.

In one embodiment, the plasma reactor further comprises a processorcontrolling the plural switches individually in accordance withuser-defined instructions.

In one embodiment, the plasma reactor further comprises a process gassource and a gas distributor comprising plural valves coupled betweenthe process gas source and respective ones of the plural cavities. Theprocess gas source may comprise plural gas sources of different gasspecies, wherein respective ones of the plural valves are coupledbetween respective ones of the plural gas sources and respective ones ofthe plural cavities. In one embodiment, the plasma reactor furthercomprises a processor controlling the plural valves individually inaccordance with user-defined instructions.

In one embodiment, the plasma reactor further comprises a remote plasmasource coupled to deliver plasma by-products to the plural cavities.

In one embodiment, the processing chamber further comprises acylindrical side wall, the reactor further comprising an inductivelycoupled plasma source comprising a coil antenna wound around thecylindrical side wall and an RF power generator coupled to the coilantenna through an impedance match.

In one embodiment, a plasma reactor comprises: a processing chamber anda workpiece support in the processing chamber; a gas distributoroverlying the workpiece support; plural cavity walls defining pluralcavities underlying the gas distributor, the gas distributor comprisingplural gas flow paths to respective ones of the plural cavities;respective power applicators adjacent respective ones of the pluralcavities, a power source, plural power conductors coupled to respectiveones of the power applicators, and a power distributor coupled betweenthe power source and the plural power conductors; and a process gassource and a gas distributor comprising plural valves coupled betweenthe process gas source and respective ones of the plural cavities.

In a further embodiment, a method of processing a workpiece in a plasmareactor comprising an array of plasma point sources distributed over asurface of the workpiece, comprises: performing a plasma process on theworkpiece; observing a non-uniformity in a spatial distribution ofprocess rate across the surface of the workpiece; and reducing thenon-uniformity by performing at least one of:

(a) adjusting an apportionment of plasma source power levels among thearray of plasma point sources, or(b) adjusting an apportionment of gas flows among the array of plasmapoint sources.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the exemplary embodiments of the presentinvention are attained can be understood in detail, a more particulardescription of the invention, briefly summarized above, may be had byreference to the embodiments thereof which are illustrated in theappended drawings. It is to be appreciated that certain well knownprocesses are not discussed herein in order to not obscure theinvention.

FIG. 1A is a simplified diagram of a first embodiment having an array ofplasma point sources.

FIG. 1B is an enlarged plan view of a plasma point source in theembodiment of FIG. 1A.

FIGS. 2A and 2B depict different arrangements of an array of plasmapoint sources.

FIG. 3 depicts an embodiment in which the plasma point sources employplasma D.C. discharge.

FIG. 4 depicts an embodiment in which the plasma point sources employinductive coupling.

FIG. 5 depicts a modification of the embodiment of FIG. 1A employing aremote plasma source.

FIG. 6 depicts a modification of the embodiment of FIG. 4 employing aremote plasma source.

FIG. 7 depicts a modification of the embodiment of FIG. 1A having achamber-wide inductively coupled source in addition to the array ofplasma point sources.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation. It is to be noted, however, that the appendeddrawings illustrate only exemplary embodiments of this invention and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

DETAILED DESCRIPTION Introduction

A plasma source consists of a multitude or array of independentlycontrolled local plasma point sources, which allows the spatial andtemporal control of charged particle species (electrons, negative andpositive ions) and radicals over a user defined region.

Using a plasma source that enables spatial and temporal control enablescorrection of local non-uniformities. This may be accomplished byswitching ON or OFF plasma generation in different plasma point sourceswhere the charged particles and radicals are generated. Alternatively orin addition, this may be accomplished by changing process gas flows tothe different plasma point sources. For example, the gas flow may beswitched ON or OFF and/or the gas mixture for each plasma point sourcemay be changed. The user can select the gas to be ionized or broken downin the local plasma point source. The user can further select the timeor duration of the discharge.

One can alter the local discharge chemistry by either operating inparallel different gas chemistries in different simultaneous local gasdischarges (spatial control) or by alternating gas chemistry locally inthe same local discharge.

One can subject the entire workpiece (wafer) to a constant negative DCbias but attract ions locally to implant, or etch or deposit.

The array of plasma point sources can be combined with a conventionalnon-local plasma source (such as a capacitively coupled large electrodeplasma source or an inductively coupled plasma source) and, in realtime, correct for local non-uniformities in plasma generation.

The array of plasma point sources can be combined with a remote plasmasource (e.g., a remote radical source). The radical processing stepcould be followed by a plasma treatment step where one can vary thecomposition and local dwell time. Past solutions have focused on localvariation of temperature by varying current through local heatingelements in the substrate holders. Embodiments described herein add tothe existing solution, and enable local chemistries, and affect thegeneration of charged particles and radicals rather than depending upononly temperatures to speed up reactions.

Embodiments

FIGS. 1A and 1B depict an embodiment having multiple plasma pointsources 90 that are capacitively coupled using an RF frequency. Thepoint sources 90 can be arranged in various configurations, such ascircular (FIG. 2A) or pie shaped (FIG. 2B). The embodiment of FIG. 1Aincludes a process chamber body 100 having a processing zone 92 enclosedby a cylindrical side wall 102, a lower ceiling 104 and a floor 106. Aworkpiece support 94 supports a workpiece 96 within the processing zone92. A vacuum pump 108 may be coupled to the processing zone 92 throughthe floor 106. An upper ceiling 110 supported on an upper cylindricalside wall 126 overlies the lower ceiling 104 and supports a gasdistributor 112. The lower ceiling 104 includes an array of gas outletholes 114. In the embodiment of FIG. 1A, the point sources 90 are anarray of cylindrical cavities 115 enclosed by dielectric cylindricalcavity walls 116, each being parallel to an axis of symmetry of thecylindrical side wall 102 and aligned with a respective one of the gasoutlet holes 114. The dielectric cylindrical cavity walls 116 are ringedby respective cylindrical electrodes 118.

Each plasma point source 90 is local, in that the area of each gasoutlet hole 114 is small relative to the area of the lower ceiling 104or the upper ceiling 110 or relative to the diameter of the chamber body100. In one embodiment, the area of each gas outlet hole 114 does notexceed 5% of the area of the lower ceiling 104 or the upper ceiling 110or area of the chamber body 100.

In the illustrated embodiment of FIGS. 1A and 1B, the shape of each gasoutlet opening 114 is circular and conforms with the shape of thecylindrical cavity 115. However, in other embodiments, each gas outlethole 114 may be of any shape and may not conform with the shape of thecylindrical cavity 115. For example, each gas outlet hole 114 may be ofa non-circular shape (e.g., elliptical) or may be of a polygonal shapeor a linear slot shape or combinations of some of the foregoing shapes.If the shape of the gas outlet hole 114 does not conform with thecylindrical cavity 115, then an adapter (not illustrated) may beintroduced to provide a gas seal between the gas outlet hole 114 and thecylindrical cavity 115, in one embodiment.

The upper ceiling 110 has an array of gas inlet openings 119 eachaligned with a respective one of the cylindrical cavities 115. The gasdistributor 112 furnishes process gases into the cylindrical cavities115 through the gas inlet openings 119. Individual power conductors 120conduct power to individual ones of the respective cylindricalelectrodes 118. A power distributor 122 distributes power to the powerconductors 120 from a power source 124. In one embodiment, the powersource 124 is an alternating current (AC) power generator or a radiofrequency (RF) power generator with an RF impedance match. In relatedembodiments, the frequency of the power source 124 may be any from D.C.to UHF, for example. In one embodiment, plasma is produced in thecylindrical cavities 115 by capacitive coupling of RF power from thecylindrical electrodes 118 through the dielectric cylindrical cavitywalls 116 into the cylindrical cavities 115. The lower ceiling 104isolates the cylindrical electrodes 118 from plasma.

The gas distributor 112 receives different gas species from plural gassupplies 250 and apportions different gas mixtures to different ones ofthe cylindrical cavities 115 through the respective gas inlet openings119 in accordance with different user-specified gas recipes for thedifferent cylindrical cavities 115. For example, the gas distributor 112may include an array of gas valves 252 individually controlled by aprocessor 254 in accordance with user-defined instructions that definegas mixtures for the individual cylindrical cavities 115. The array ofgas valves 252 is coupled between the plural gas supplies 250 and thegas inlet openings 119 to the cylindrical cavities 115.

The power distributor 122, in one embodiment, controls the powersupplied to each power conductor 120 individually. For example, thepower distributor 122 may include an array of electrical switches 262individually controlled by the processor 254 in accordance withuser-defined instructions. The power may be controlled by pulse widthmodulation, and the user-defined instructions may define individualon/off durations (or duty cycles) of power for the individualcylindrical cavities 115. The array of electrical switches 262 iscoupled between the power source 124 and the power conductors 120.

In a first embodiment, the lower ceiling 104 is formed of a dielectricmaterial while the upper ceiling 110 is formed of a conductive material.In a second embodiment, the lower ceiling 104 is adjacent a lower plate190 formed of a conductive material, and both the lower plate 190 andthe upper ceiling 110 are grounded. In this way, the plasma source islocated between two grounded plates, namely the lower plate 190 and theupper ceiling 110.

FIG. 3 depicts an embodiment in which plasma is produced by a D.C.discharge, and the power source 124 is a D.C. power generator. Each ofthe dielectric cylindrical cavity walls 116 is terminated above thecorresponding one of the cylindrical electrodes 118. This feature candirectly expose each cylindrical electrode 118 to plasma to facilitatethe D.C. discharge.

FIG. 4 depicts a modification of the embodiment of FIG. 1A, in which thecylindrical electrodes 118 are replaced by individual inductive coils210, to produce an inductively coupled plasma within each cylindricalcavity 115. Each inductive coil 210 is wrapped around a bottom sectionof the corresponding cylindrical dielectric wall 116, as depicted inFIG. 4. In the embodiment of FIG. 4, a changing magnetic field generatesa changing electric field in the cylindrical cavity 115 which in turngenerates a closed turn oscillating plasma current.

FIG. 5 depicts another modification of the embodiment of FIG. 1A thatincludes a remote plasma source 220 and a radical distribution plate280. The radical distribution plate 280 directs radicals from the remoteplasma source 220 into the individual cylindrical cavities 115. Theremote plasma source 220 may include a plasma source power applicator222 driven by a power source 224. The remote plasma source 220 mayfurther include controlled gas sources 226 containing precursors ofdesired radical species. There are some processes in which chemicallyactive radicals generated remotely play a critical role in theprocessing of wafers. However, there may be a need to follow the radicaltreatment with a plasma treatment step. Having a spatially andtemporally controllable plasma source helps in addressing radicalnon-uniformity. In the case of radicals which are short lived (recombineinto inert neutrals), having a controllable plasma density can helpregenerate important radicals.

FIG. 6 depicts a modification of the embodiment of FIG. 4 that includesa remote plasma source 220 and a radical distribution plate 280. In theembodiment of FIG. 6, the remote plasma source 220 is combined with theinductively coupled plasma sources (i.e., the inductively coupled coils210) of FIG. 4. The inductively coupled plasma sources (the coils 210)enable operation in different (lower) pressure regimes (e.g., below 25mTorr), compared to the capacitively coupled plasma source of theembodiment of FIG. 1A.

FIG. 7 depicts a modification of the embodiment of FIG. 1A, in which thearray of plasma point sources 90 is combined with a larger non-localinductively coupled plasma source. The non-local inductively coupledplasma source of FIG. 7 includes a helically wound coil antenna 240surrounding the cylindrical side wall 102. The helically wound coilantenna 240 is driven by an RF power generator 242 through an RFimpedance match 244. In the embodiment of FIG. 7, the cylindrical sidewall 102 is formed of a non-metallic material to enable inductivecoupling of RF power through the cylindrical side wall 102. The lowerplate 190 protects the individual plasma point sources (corresponding tothe individual cylindrical cavities 115) from the larger inductivelycoupled plasma source (corresponding to the helically wound coil antenna240).

The individual plasma point sources 90 (corresponding to the individualcylindrical cavities 115) are individually controllable. The enablesspatial and temporal control of plasma distribution. Such control may beexercised in such a manner as to reduce plasma distributionnon-uniformity.

Control Modes:

The power source 124 can power each plasma point source 90 in differentmodes. In a first mode, each plasma point source 90 dissipates a fixedamount of power and the control system switches on or off the powerfurnished to the plasma point source using the array of electricalswitches 262. In one example, each point source dissipates a constantamount of about 3 watts when it is on. The array of electrical switches262 essentially apply the power to individual plasma point sources 90 oncommand. The plasma density is a function of how many plasma pointsources 90 are turned on. In this manner, the net power delivered toeach plasma point source 90 may be controlled by pulse widthmodification.

In a second mode, what is controlled is the level of power delivered toeach plasma point source 90. Also, gas composition to individual plasmapoint sources 90 (or groups of plasma point sources 90) can be varied bythe gas distributor 112. Thus, the different plasma point sources 90need not have the same gas discharge composition. Each plasma pointsource 90 has a fixed address. The power and/or gas flow to each plasmapoint source 90 can be targeted to turn on or off individually.

In accordance with one method, the spatial distribution of process rateacross the surface of the workpiece is measured. The non-uniformities inthe process rate distribution are compensated by establishing a spatialdistribution of ON/OFF duty cycles of power supplied to the array ofplasma point sources 90 that is in effect an inverse of the measuredprocess rate spatial distribution. In other words, the distribution ofON/OFF power duty cycles has maxima in locations where the measuredprocess rate distribution has minima and has minima where the measuredprocess rate distribution has maxima.

In accordance with another method, the non-uniformities in the processrate distribution are compensated by establishing a spatial distributionof ON/OFF duty cycles of process gas flows supplied to the array ofplasma point sources 90 that is in effect an inverse of the measuredprocess rate spatial distribution. In other words, the distribution ofON/OFF gas flow duty cycles has maxima in locations where the measuredprocess rate distribution has minima and has minima where the measuredprocess rate distribution has maxima.

Advantages:

A primary advantage is complete control spatially and temporally of thegeneration of charged particles and energetic radicals. This enablesspatial and temporal control over distribution of local chargedparticles and energetic radicals.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A plasma reactor comprising: a processing chamberand a workpiece support in said processing chamber, said chambercomprising a lower ceiling facing said workpiece support; an upperceiling overlying and facing said lower ceiling and a gas distributoroverlying said upper ceiling; plural cavity walls defining pluralcavities between said upper and lower ceilings, said gas distributorcomprising plural gas flow paths to respective ones of said pluralcavities; plural outlet holes in said lower ceiling aligned withrespective ones of said plural cavities; respective power applicatorsadjacent respective ones of said plural cavities, a power source, pluralpower conductors coupled to respective ones of said power applicators,and a power distributor coupled between said power source and saidplural power conductors.
 2. The plasma reactor of claim 1 wherein saidplural cavity walls comprise dielectric cavity walls.
 3. The plasmareactor of claim 1 wherein said power source comprises an RF powergenerator and wherein each one of said respective power applicators isseparated from an interior of a corresponding one of said pluralcavities by the corresponding one of said plural cavity walls.
 4. Theplasma reactor of claim 3 wherein said power applicator comprises anelectrode for capacitively coupling RF power into the corresponding oneof said plural cavities.
 5. The plasma reactor of claim 4 wherein saidelectrode surrounds a section of the corresponding one of said pluralcavities.
 6. The plasma reactor of claim 3 wherein said power applicatorcomprises a coil antenna for inductively coupling RF power into thecorresponding one of said plural cavities.
 7. The plasma reactor ofclaim 6 wherein said coil antenna comprises a conductor coiled around asection of the corresponding one of said plural cavities.
 8. The plasmareactor of claim 1 wherein said power source is a D.C. power generator,each one of said power applicators comprises an electrode for D.C.discharge, and wherein each one of said cavity walls is configured toexpose a corresponding electrode to an interior of a corresponding oneof said plural cavities.
 9. The plasma reactor of claim 1 wherein saidpower distributor comprises plural switches coupled between an output ofsaid power source and respective ones of said power conductors.
 10. Theplasma reactor of claim 9 further comprising a processor controllingsaid plural switches individually in accordance with user-definedinstructions.
 11. The plasma reactor of claim 1 further comprising: aprocess gas source and a gas distributor comprising plural valvescoupled between said process gas source and respective ones of saidplural cavities.
 12. The plasma reactor of claim 11 wherein said processgas source comprises plural gas sources of different gas species,wherein respective ones of said plural valves are coupled betweenrespective ones of said plural gas sources and respective ones of saidplural cavities.
 13. The plasma reactor of claim 12 further comprising aprocessor controlling said plural valves individually in accordance withuser-defined instructions.
 14. The plasma reactor of claim 9 furthercomprising: a process gas source and a gas distributor comprising pluralvalves coupled between said process gas source and respective ones ofsaid plural cavities.
 15. The plasma reactor of claim 14 wherein saidprocess gas source comprises plural gas sources of different gasspecies, wherein respective ones of said plural valves are coupledbetween respective ones of said plural gas sources and respective onesof said plural cavities.
 16. The plasma reactor of claim 15 furthercomprising a processor controlling said plural valves individually andcontrolling said plural switches individually in accordance withuser-defined instructions.
 17. The plasma reactor of claim 1 furthercomprising a remote plasma source coupled to deliver plasma by-productsto said plural cavities.
 18. The plasma reactor of claim 1 wherein saidprocessing chamber further comprises a cylindrical side wall below saidlower ceiling, said reactor further comprising an inductively coupledplasma source comprising a coil antenna wound around said cylindricalside wall and an RF power generator coupled to said coil antenna throughan impedance match.
 19. A plasma reactor comprising: a processingchamber and a workpiece support in said processing chamber; a gasdistributor overlying said workpiece support; plural cavity wallsdefining plural cavities underlying said gas distributor, said gasdistributor comprising plural gas flow paths to respective ones of saidplural cavities; respective power applicators adjacent respective onesof said plural cavities, a power source, plural power conductors coupledto respective ones of said power applicators, and a power distributorcoupled between said power source and said plural power conductors; anda process gas source and a gas distributor comprising plural valvescoupled between said process gas source and respective ones of saidplural cavities.
 20. A method of processing a workpiece in a plasmareactor comprising an array of plasma point sources distributed over asurface of the workpiece, comprising: performing a plasma process on theworkpiece; observing a non-uniformity in a spatial distribution ofprocess rate across the surface of the workpiece; and reducing saidnon-uniformity by performing at least one of: (a) adjusting anapportionment of plasma source power levels among said array of plasmapoint sources, or (b) adjusting an apportionment of gas flows among saidarray of plasma point sources.